The present invention relates to a diagnosis device for determining whether or not an internal combustion engine exhaust gas recycling device used in a vehicle such as an automobile is functioning correctly, and particularly relates to a diagnosis device which carries out reliable fault diagnosis regardless of changes in the environmental conditions.
In an internal combustion engine used in a vehicle such as an automobile, in order to reduce the NOx in the exhaust gas, conventionally various types of exhaust gas recycling devices have been incorporated to recycle the exhaust gas. Such an exhaust gas recycling device is disclosed in for example Japanese Utility Model Laying Open Publication Sho No. 54-121116 (1979), Japanese Patent Laying Open Publication Sho No. 58-88450 (1983), and Japanese Patent Publication Sho No. 60-24303 (1985).
Generally an exhaust gas recycling device incorporates an exhaust gas recycling control valve for controlling the recycling flow rate of the exhaust gas, a vacuum control valve for controlling the background pressure, a temperature sensing valve, and so forth, and if there is a fault in any of these structural components, the exhaust gas recycling will no longer be carried out and there is a danger of the internal combustion engine beeing operated in a state where the reduction in NOx in the exhaust gas is not carried out. Even if the exhaust gas recycling is not carried out because of a failure, the internal combustion engine will still operate without failing, and may therefore be driven for a long time without the driver realizing; this gives rise to atmospheric pollution problems. Additionally, in certain operating conditions, if exhaust gas recycling is not carried out then there is a danger of knocking occurring, and also it is possible for the fuel consumption to be worsened by pump loss from the intake of the internal combustion engine itself.
In view of the above situation, a failure alarm device has already been proposed constructed such that when the exhaust gas recycling has stopped because of a failure of the exhaust gas recycling device the user is informed and given an opportunity for repair, and this is disclosed in for example Japanese Utility Model Laying Open No. Publication Sho 49-64623 (1974) (Japanese Utility Model Publication Sho No. 52-9471 (1977), in Japanese Utility Model Laying Open Publication Sho No. 50-67220 (1975), and also in Japanese Utility Model Application Sho No. 60-163288 (1985) (Japanese Utility Model Laying Open Publication Sho No. 62-7163 (1987) by the same applicant as the applicant in the present application.
Fault diagnosis of the exhaust gas recycling device may be carried out basically by, under conditions in which exhaust gas recycling should be carried out, determining whether or not, for example, the temperature within an exhaust gas recycling passage is at least a certain value, in other words by determining that if that temperature is not more than a cetain value exhaust gas is not flowing in the exhaust gas recycling passage, and thus determining that the exhaust gas recycling device has failed, but if it is simply supposed that exhaust gas recycling should be carried out when various parameters indicating operating conditions such as the intake pressure or intake flow rate of the internal combustion engine or the engine rotation speed, have certain values, then when the atmospheric pressure fluctuates because of for example high altitude driving, since the intake pressure will fluctuate correspondingly, the conditions for exhaust gas recycling will not be determined appropriately, and there is a danger that the fault diagnosis of the exhaust gas recycling device will not be carried out correctly. Particularly when the exhaust gas recycling control is carried out from the intake pressure, the ranges of intake pressure and engine revolution rates in which exhaust gas recycling are carried out will fluctuate according to the atmospheric pressure fluctuation.
Fault diagnosis of the exhaust gas recycling device may be carried out basically by, under conditions such that exhaust gas recycling should be carried out, determining whether or not, for example, the temperature within an exhaust gas recycling passage is at least a certain value, in other words by determining that when the exhaust gas recycling passage temperature is not more than a certain value exhaust gas is not flowing in the exhaust gas recycling passage, and thus determining that the exhaust gas recycling device has filed, but when the exhaust gas recycling is started the temperature within the exhaust gas recycling passage does not rise rapidly, and moreover this temperature rise is further delayed the lower the outside temperature. Therefore a false diagnosis may easily be made if the fault diagnosis is carried out simply by determining if the exhaust gas recycling passage temperature is at least a certain value under conditions in which exhaust gas recycling should be carried out.
The present invention considers the above state of affairs, and has as its object the provision of an improved exhaust gas recycling device diagnosis device which carries out accurate fault diagnosis always with no erroneous diagnoses even if the atmospheric pressure fluctuates or the outside air temperature fluctuates.